A novel bioengineered technique to rapidly and permanently repair cut PNS nerves Our long term objective is to performance-optimize to translate for clinical use our novel and innovative technique to produce rapid and permanent repair of acutely and chronically severed mammalian PNS axons to restore the behavioral functions they mediated prior to severance. We apply a well-specified sequence of bioengineered solutions containing polyethylene glycol (PEG) and various anti-oxidizing or oxidizing agents to rapidly and permanently rejoin (PEG-fuse) completely cut-severed ends of rat sciatic axons as a model in vivo system so that PEG-fused axons are physiologically and morphologically intact through the lesion site and their stimulation restores behavioral functions mediated by intact sciatic nerves. Our physiological and morphological measures of axonal continuity are action potential conduction and intraaxonal dye diffusion across the lesion site and EM and immuno-histochemical analyses.. Our measures of behavioral restoration are Foot Fault Asymmetry test and Sciatic Functional Index. We retard Wallerian degeneration by cooling or cyclosporin A and then repair axons chronically severed for up 10 days by PEG-fusion. We performance optimize tissue (biocompatability) responses of acutely or chronically excised sciatic nerve segments that are used as inter- position autografts or allografts to PEG-fuse repair acutely or chronically cut rat sciatic nerves. Nerve severance is a common traumatic injury to PNS axons in humans. Various procedures currently slightly improve the number and specificity of PNS axons that reestablish connections following severance, but not outgrowth rate (~1mm/day) or time (weeks to years) for PNS axons to re-establish those connections. Target tissues may atrophy before re-innervation can occur. Consequently, target tissues are often non-specifically re-innervated and behavioral recovery is often poor. PEG-fusion dramatically improves the speed and efficacy of behavioral recovery following acute cut- or crush-severance of mammalian PNS axons. We can also retard axonal Wallerian degeneration of severed mammalian axons for up to 10 days to increase the time for successful PEG-fusion for up to 10 days post-severance so that nerve injuries do not have to be immediately treated. Our well-specified sequence of bio-engineered solutions and materials needed for PEG-fusion use only FDA-approved chemicals. Hence, our PEG-fusion technique developed on rat sciatic nerves as a model in vivo system should rapidly translate to clinical procedures. The results of our proposed R-01 have high potential for shifting the current emphasis of current research and clinical practice from devising procedures to enhance the results of slow axonal outgrowth to considering rapid repair by our novel PEG-fusion technique.